HANDBOOK FOR BIO-CHEMICAL LABORATORY. 89 



PENZOLDT and FISCHER'S Test (Phenol). On treating a 

 strongly alkaline solution of phenol with a solution of diazo- 

 benzol sulphonic acid a deep red coloration is the result. 



PEPTONES. See Hofmeister. 



PETRI'S Test (Proteids). On treating a proteid or peptone 

 solution with a solution of diazobenzol sulphonic acid only a 

 faint yellow coloration is produced, but on making the solu- 

 tion alkaline with caustic alkali the solution becomes orange 

 yellow to brown, according to concentration, and yields a red 

 froth on shaking. 



PETTEN KOFER'S Test (Bile Acids). A small quantity of bile 

 in substance is dissolved in a small porcelain dish in con- 

 centrated sulphuric acid and warmed, or some of the liquid 

 containing the bile acids is mixed with concentrated sul- 

 phuric acid, taking special care in both cases that the tem- 

 perature does not rise higher than 60-70 C. Then a 10$ 

 solution of cane-sugar is added, drop by drop, continually 

 stirring with a glass rod. The presence of bile is indicated by 

 the production of a beautiful red liquid, whose color does not 

 disappear at the ordinary temperature, but becomes more blu- 

 ish violet in the course of a day. This red liquid shows a 

 spectrum with two absorption-bands, the one at F and the 

 other between D and E, near E. 



PHENOL. See Allen, Bertlielot, Davy, Eijkmann, Jacque- 

 min, Landolt, Penzoldt and Fischer. 



PIOTROWSKI'S Reaction (Proteids), also called Biuret Re- 

 action. On heating a proteid with an excess of a concen- 

 trated solution of caustic soda and one or two drops of a 

 dilute solution of copper sulphate a violet color is produced 

 which deepens in tint on boiling. 



